1. Field of the Invention
The invention relates generally to surface treating machines and, more particularly, to an improved portable blast machine for cleaning substantially vertical surfaces.
2. Description of the Related Art
Blast cleaning machines typically consist of a blast wheel having a plurality of blades extending radially therefrom. The blast wheel is mounted in a housing and is rotatably driven at high speed. Abrasive such as steel shot is fed onto the blades and is projected against the surface to be cleaned. The impact of the abrasive with the surface to be cleaned dislodges paint, rust and other debris from the surface. Typically, the debris is removed from the system and the spent abrasive is recirculated back to the blast wheel. The housing is typically moved along over the surface to be cleaned.
A particularly useful application of portable blast cleaning machines is the cleaning of large vertical surfaces, such as the outer side walls of a ship's hull or a large tank for storing water, gas or the like. Such portable blast machines are usually suspended by cables from a movable hoist positioned above the vertical surface. The hoist raises and lowers the device vertically and moves horizontally so that the device may traverse the vertical surface.
Examples of such machines are presented by Diehn, U.S. Pat. No. 3,900,969; Bergh, U.S. Pat. No. 4,020,596; and Van Fossen, U.S. Pat. No. 4,319,436. The machines disclosed by these patents all feature a blasting wheel that projects abrasive upwardly at the vertical surface. The abrasive rebounds off of the vertical surface, taking the debris that was removed from the surface, such as paint and rust, and dust with it. The rebounding mixture of abrasive, debris and dust enters a rebound passage and then a filtering passage where it is exposed to an air stream that removes the debris and dust but leaving the heavier abrasive. The separated debris and dust are carried away by the air stream for deposit in a drum on the ground while the abrasive falls into a hopper within the device where it is returned to the blast wheel for reuse.
A disadvantage of such designs is that the angled orientation of the blast wheel and the rebound chamber limit the compactness of the devices. More specifically, in order for the blast wheel to project the abrasive against the vertical surface at the proper angle, it must be oriented and spaced a certain distance away from and below the portion of the vertical surface being treated. Furthermore, a somewhat lengthy chamber must lead from the blast wheel to the vertical surface. In addition, the rebound passage must be nearly perpendicular to the initial blast path. These requirements lead to devices having V-shaped housings that are not space efficient.
A device that is more space efficient is desirable in that it would be more compact and lightweight. This would allow the device to be more easily transported, carried and handled. For example, a lighter duty, and thus less expensive, hoist could be used to raise and lower the device. A more compact device could also more easily and thoroughly access confined spaces such as comers and portions of the vertical surface that are close to the ground. In addition, due to its compact design, such a machine could be manufactured at a lower material cost. As such, it is an object of the present invention to provide an improved portable blast wheel cleaning machine that is compact and lightweight.
In the use of portable blast machines to clean vertical surfaces, it is desirable to confine the space about the surface being treated to permit recovery of abrasive and to prevent the development of hazardous conditions resulting from the ricocheting of particulate material into the surrounding atmosphere. In a portable device that is being moved over a vertical surface, the device housing obviously cannot be permanently attached to the surface to effect the desired sealing relation. As a result, flexible seals made of rubber or polyurethane are often deployed around the blast opening of the device so as to be positioned between the device housing and the vertical surface. Such seals are limited in effectiveness, however, by uneven vertical surfaces and wear of the seals themselves.
Accordingly, it is desirable to have a system whereby particulate material that leaks from the seals may be recovered. As such, it is a further object of the present invention to provide an improved portable blast wheel cleaning machine wherein particulate which escapes the seals may be recovered.